The invention relates to a device for forming objects in a cavity which is at least partially formed by an insert in a mold plate.
In the injection-molding process for example, objects are produced by filling a cavity in a mold, for example with thermoplastic materials. This forming operation must be monitored as it proceeds. For example, the filling operation is controlled in such a way that an initial speed-controlled phase is followed by a pressure-controlled phase, which lasts until the end of the filling operation. Toward the end of the speed-controlled phase or in the initial period of the pressure-controlled phase, the filling situation in which the mold cavity is completely wetted with plasticizable compound is reached, the pressure of the compound inside the mold cavity still being relatively low. As a result of the continuation of the movement of an injection plunger or an extruder, this is followed by an increase in the internal mold pressure, accompanied by a reduction in the specific volume or an increase in the density of the molding compound located in the mold cavity. The extent of the compaction which can be achieved in this way depends not only on the prevailing temperature but also on the level of the pressure acting and the characteristic properties of the molding compound.
In particular for quality assurance, process optimization, process monitoring and process control purposes, pressure and temperature sensors are used, fitted in the injection mold in such a way that the sensor front contacts the plastic part to be produced. Such an arrangement is described for example in DE 101 14 228 A1. For measuring piezoelectric signals, highly insulating lines are generally used.
There are molds in which the part of the mold that forms part of the cavity is formed directly from a mold plate or in a mold plate. Usually used for this purpose, however, is an insert in a mold plate that can be exchanged, for example if it becomes worn or there is a design modification. The actual mold plate remains the same, only the insert is replaced.
There are also instances in which inserts have to be exchanged and replaced by other inserts within an extremely short time during production, in order to produce new molded parts with new geometries. In such instances, the injection mold that is clamped on the machine continues to be used unchanged, while only the mold inserts are replaced. It is even conceivable for the change of such an insert to be performed fully automatically with the aid of a robot.
In practice, not only injection molds with a single mold cavity and a single mold insert are used but also multi-cavity molds with a mold insert respectively for each cavity. Here, too, these mold inserts are exchanged in the way described above for various reasons.
The present invention is based on the problem of providing a device of the aforementioned type with which sensors, in particular for pressure and temperature, can be used even in the case of molds in which the cavities are formed by inserts.